I am making a small 9V battery powered synthesizer with a square wave oscillator built around a 40106b Schmitt trigger (reference: http://richdecibels.com/blog/?p=11) and a few other components, one of which is a white noise generator (similar to this build: https://www.flickr.com/photos/secondhandsynth/4501573713/)

My problem is, the square wave oscillator is bleeding into every part of the circuit. It's really loud, and its leaking into other sound generators on the circuit board that it's not even connected to in any way besides power and ground. As I probe the circuit board with a speaker input, I can hear the oscillator ring through every part of the build.

Is there a way to isolate a loud oscillator from the rest of the circuit? Or prevent signals from cross-talking on a common ground?


  • 1
    \$\begingroup\$ Did you decouple the 40106 power supply lines with a 100nF capacitor and leads as short as possible? \$\endgroup\$
    – jippie
    May 10, 2014 at 20:32
  • \$\begingroup\$ Leads are short: I took the project off the breadboard and am playing with it soldered together. How do I decouple with a capacitor? thanks \$\endgroup\$
    – pinhead
    May 10, 2014 at 20:34
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    \$\begingroup\$ Here are some other answers about using decoupling capacitors: electronics.stackexchange.com/q/2262/2028, electronics.stackexchange.com/q/2272/2028 \$\endgroup\$
    – JYelton
    May 10, 2014 at 20:39
  • \$\begingroup\$ In addition to decoupling caps, you'll also want a largish (10 to 100 uF) tantalum cap on the 9 volt line. 9 volt batteries don't have a terribly small ESR, so a cap is always a good idea. \$\endgroup\$ May 10, 2014 at 21:10
  • \$\begingroup\$ I am not typing about the capacitor used for the oscillators, but about power supply decoupling. @WhatRoughBeast Tantalum caps are not a good fit for the inexperienced, they can selfdestroy violently (much more than a regular electrolytic cap) when used in a wrong way or slightly out of spec. For a simple circuit as this, regular (electrolytic) caps will do just fine. \$\endgroup\$
    – jippie
    May 10, 2014 at 21:13

1 Answer 1


Decouple the power supply lines with a 100nF capacitor. Keep the leads short for maximum effect.


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